The invention relates to a laminar-flow centrifugal separator.
This separator has been devised for fluid mixtures containing solids, liquids or gases in varied proportions, but above all mixtures containing solid suspensions in liquid phases, to be separated into at least one liquid fraction and one fraction containing the solid. Good separation of the constituents of the mixture is then sought and a solid fraction presented in a compact form, or cake, with a relatively low residual suspension liquid content is obtained. Even when the formation of a cake gives rise to a high flow resistance, or a significant sectional reduction thereof, it is generally sought to extract this solid fraction from the separator, and if possible in a continuous fashion despite the compact nature thereof, as it is formed in the rotary bowl, without enabling same to accumulate therein. This aim is not generally achieved with existing separators, many of which require on the contrary periodic process shutdowns, adverse to the yield thereof, to remove the cake. Separators envisaging continuous removal of the solid fraction are not normally suitable for obtaining a sufficient dry content.
Indeed, numerous centrifugal separators exist. Mention is made of the document WO-A-2007/133 161, describing a separator having some superficial resemblances with the invention. It comprises as a main part a biconical rotary bowl wherein separation is performed. The mixture is introduced into the bowl via a hollow conduit, corresponding to the bowl support and rotation axis. The heavier solid fraction is routed to the periphery of the bowl and more particularly into the bulging area corresponding to the cone junction. Opening peripheral bores at this point make it possible to extract said fraction, while the fluid fraction rises towards to the top of the bowl, as the mixture is added, and is discharged via an opening situated at the top of the bowl opposite the feed opening. Conical structures, referred to as dishes, flaring at the bottom and actuated at the same time as the wall of the bowl, occupy most of the inner volume thereof They are used to partition various portions of the mixture and help homogenise the separation conditions inside the bowl. However, this device is not suitable for obtaining a solid fraction that is as homogeneous or compact as that sought, and continuous extraction of this fraction is difficult.
Mention may also be made of the document WO-A-2012/025416, describing a separator wherein the chamber is also occupied by separation dishes, however perforated in places to clear the axial channels favouring axial flow of the fluid load, and the distribution thereof in the stack of dishes. A centripetal movement of the fluid is however imposed in the bowl between radially external inlet orifices and radially internal outlet orifices, which further essentially provides flow channelling in separate parallel streams and thus differs little from the design of the previous document. The fluid is separated from the solid fraction, emerging from the peripheral wall of the bowl via lateral openings and is deposited on an outer screw actuated by this wall. A further rotating wall, but at a slightly different speed, encompasses the screw and retains the solid fraction while allow the screw to run thereon and finally leave the device due to the different rotational speed thereof. Here again, fraction separation is not very effective.
In the field of apparatuses providing a rotating outer enclosure, satisfactory drainage performances are obtained with the equipment from WO-A-2009/005355 and WO-A-2011/028122 integrating an internally lined rotation mode and a barrel-shaped outer enclosure. The internal lining consists of dishes or plates in a spiral arrangement. The use of a laminar flow is never envisaged or mentioned as an enhancement option.
Dish separators have been the subject of enhancements to prevent the accumulation of solid matter and the appearance of unbalance in the centrifuge. One proposed solution consists of perforating the dishes or placing separation disks at the lower and upper part of the lining (WO-A-2012/033440). This type of development relates more particularly to low-concentration liquid and gas treatment (scrubbing).